One of the most important classes of indicators are the biological indicators (BI). Biological indicators provide the highest degree of assurance that sterilization conditions were met throughout the processed load. This type of indicator is meant to represent the worst case for the processing system by providing within or on the indicator an extremely high number of organisms highly resistant to that particular process. Usually bacterial spores are the organism of choice for monitoring sterilization systems.
Biological indicators typically consist of microorganisms inoculated onto a carrier material. The microorganisms are typically bacterial spores that are known to be very resistant to the particular sterilization medium in which they are to be used. The carrier material can range from paper to plastic to stainless steel and may be in a variety of configurations ranging from flat surfaces to containers such as vials. Biological indicators that consist of vials and caps are known as self-contained biological indicators (SCBIs) because they contain all the elements required to process, activate and incubate the samples. The carrier is placed into a sterilization cycle along with the medical device load. Following completion of the cycle the biological indicator is incubated and monitored for growth for up to seven days. Growth of a biological indicator indicates that the sterilization process was not adequate to attain complete sterilization and that the medical device load needs to be reprocessed before use. No growth of a biological indicator confirms that conditions within the sterilizer were adequate to kill at least the number of bacterial spores loaded onto the indicator (e.g., 106 bacterial spores) and therefore provides a level of assurance that the medical device load is sterile.
The resistance of biological indicators to a particular sterilization process is determined both by the spore utilized and by the configuration of the biological indicator (e.g., SCBI or SCBI in a Process Challenge Device). Therefore, to change the resistance either the sporulation method needs to be altered or a new physical configuration of the biological indicator needs to be developed. Having various sporulation methods for different biological indicators used in different sterilization processes is not desirable from a manufacturing perspective. Designing a new physical configuration for a biological indicator can get costly, for example, because new molds may be needed. Therefore, it is desirable to be able to alter the resistance of a pre-existing biological indicator in a simple manner.
Vaporous hydrogen peroxide and other oxidative sterilization processes are very effective at killing even resistant organisms such as spores. This is beneficial to hospitals, since it allows many heat sensitive medical devices to be processed through sterilizers using vaporous hydrogen peroxide (VHF) and other oxidative sterilants. However, the rapid kill that results from such oxidative sterilants makes it difficult to develop biological indicators that effectively monitor very far into the sterilization cycle. That is, because when conventional biological indicators are used in oxidative sterilant sterilization processes, the organisms in the biological indicators are so rapidly killed, it is less certain that an effective dose of the oxidative sterilant has reached and been maintained at effective levels to all portions of the load of medical devices as would be the case if the indicator were killed more slowly.
Thus, a need for a solution to the previously un-solved problem of too-rapid kill of biological indicators by oxidative sterilants has existed for some time. The present invention is intended to address this problem.